The Preparation And Characteristics Of The Ferroelectric Crystals With Upconversion Properties

The Pb(Zn_1/3Nb_2/3)O₃-PbTiO₃ （PZN-9PT） single crystals have been widely used in medical ultrasonics, sensing and piezoelectric actuators because of the excellent piezoelectric coefficient and high electromechanical coupling factors. However, the application in the high temperature and power devices is restricted due to the lower rhombohedral to tetragonal phase transition and the low coercive fields. Therefore, in the present work, the influence rare-earth Ho³⁺ and Er³⁺ on the phase structure, electrical properties, dispersion degree and luminescence properties of the PZN-9PT single crystals were primarily investigated.The as-grown single crystals were grown by using the flux method. The structure, electrical properties and luminescence properties of the as-grown single crystals were characterized and analysized by using XRD, SEM, the temperature dependence of permittivity, infrared absorption and fluorescence spectrometer. The results were as the followings:The PZN-9PT and rare-earth (Ho³⁺ and Er³⁺) modified PZN-9PT single crystals with light color had the pure perovskite structure. The rare-earth Ho³⁺ and Er³⁺ could substitute for the B-sites （Zn2+ and/or Nb5+） of PZN-9PT single crystals based on the analysis of the expansion of volume and on the difference of different ionic radius. Furthermore, the rhombohedral to tetragonal phase transition temperature of the PZN-9PT single crystals were respectively increased by 12 ℃ and 7 ℃ under the modification of rere-earth Ho³⁺ and Er³⁺. The coercive field were increased by 2.4 kV/cm and 8 kV/cm, respectively.The Lorentz-type law indicated that the rare-earth (Ho³⁺ and Er³⁺) modified PZN-9PT single crystals possessed the typical characteristic of diffused phase transition under the different measuring frequency. The Lorentz-type law and modified Curie-Weiss law suggested that the dispersion degree of PZN-9PT single crystals were significantly enhanced by the modification of the rare-earth ions (Ho³⁺ and Er³⁺) when the measuring frequency was 100 kHz.The absorption bands of Ho³⁺ and Er³⁺ were observed in the Uv-Vis-NIR absorption spectrum of the rare-earth Ho³⁺ and Er³⁺ modified PZN-9PT single crystals. The downconversion and upconversion luminescence of the Ho³⁺ and Er³⁺ modified PZN-9PT single crystals were found at 491 nm and 980 nm excitation, respectively. During the down and up conversion luminescence process, the weak red bands and strong green bands were obtained. In addition, the blue bands also were obtained in the Ho³⁺ modified PZN-9PT single crystals.